Dental ceramics are increasingly prolific as restorative materials because of their esthetic appearance and their intrinsic wear resistance, thermal insulation, and biocompatibility. Unfortunately, the currently available dental ceramics are brittle in comparison to dental alloys. This lack of fracture resistance compromises their strength and reliability, resulting in decreased lifetime expectancy. Previous strategies for increasing the lifetimes of dental ceramics have focused on improving the initial strength and tolerance to future damage; however, without a mechanism for repair, damage accumulates, and failure is inevitable. In contrast, natural materials have relatively low resistance to mechanical damage, but their usefulness is maintained over time by healing any damage that is sustained before it accumulates. The overall objective of this project is study self-healing mechanisms by which dental ceramics may exhibit mechanical fatigue resistance and increased longevity. This objective will be accomplished through incorporation of smectite clay particles in hydrothermal glass to form ceramic matrix composites, which will close cracks through the swelling of reinforcing particles. The experimental materials will be designed for use in esthetic, all-ceramic dental restorations. A commercially available low fusing ceramic (Duceram LFC) will be used as the control material for investigation of the following hypotheses: l) moisture- activated swelling of clay particles is a source of increased fracture resistance, 2) a maximum mean free path of 45 mum between reinforcing particles acts as a threshold for increased fracture resistance, 3) a mean reinforcing particle size smaller than 0.39 mum will result in materials with greater translucency than currently available ceramic core materials, 4) smectite clay-reinforced porcelains will exhibit similar or superior biocompatibility compared to unreinforced dental porcelain, and 5) smectite clay-reinforced porcelains will exhibit hardness and abrasive potential lower than those of unmodified dental I porcelain. These efforts may elucidate the mechanisms of fatigue failure and may result in materials that will fill the public demand for long-lasting, esthetic dental restorations.